The majority of HIV-infected people live in resource-poor regions where instruments critical for detecting, staging, and monitoring the disease condition resulting from HIV are frequently unavailable because of difficult field conditions, cost, or lack of trained personnel, e.g. Cohen, AIDS, Suppl 4: S81-S87 (2007). This has led to the development by several groups of low-cost instrumentation designed for deployment in resource-poor settings for measuring CD4 counts in patient blood samples, e.g. Rodriguez et al, PLoS Medicine, 2(7): e182 (2005); Ymeti et al, Cytometry A 71: 132-134 (2007); Cheng et al, Lab Chip, 7(2): 170-178 (2007); Pattanapanyasat et al, Clinical Cytometry, 72B: 387-396 (2007); and the like. Although such advances have reduced costs of cell counting techniques, generally all of these approaches still require detection or sample handling systems that either have dedicated electronic or optical components needing trained operators, calibration, or external power, or other drawbacks, or still do not reduce costs to levels permitting widespread applicability.
In view of the above, several medical and biotechnology fields would be significantly advanced with the availability of techniques, capable of point-of-care operation, which permitted facile and flexible measurements of cellular markers, particularly in biological fluids, such as blood.